1. Field of the Invention
The present invention relates to an ink jet recording ink used in an ink jet recording apparatus, and to an ink jet recording method.
2. Description of the Related Art
In ink jet recording theory, a liquid or molten solid ink is discharged through nozzles, slits, porous film, and the like onto paper, cloth, film, and the like to record images. Various methods for discharging ink are suggested, such as the so-called charge-control method in which the ink is discharged using electrostatic attractive force, the drop-on-demand method (pressure-pulse method) in which ink is discharged using the vibration all pressure of a piezoelectric element, and the thermal ink jet method in which ink is discharged using pressure generated by forming and developing bubbles at high temperature, and the like. Images having extremely high resolution can be obtained using these methods.
The ink used in these ink jet recording methods include an aqueous dye ink obtained by dissolving various water-soluble dyes in a liquid medium composed of water and a water-soluble organic solvent, an aqueous pigment ink obtained by dispersing various pigments in a liquid medium composed of water and a water-soluble organic solvent, an oil-based dye ink obtained by dissolving an oil-soluble dye in an organic solvent, and the like.
Among these inks, aqueous ink with a dissolved aqueous dye is most frequently used as an ink jet recording ink. The first reason thereof is that the main solvent is water and so the aqueous ink is safe. Moreover, the second reason is that the color-developing properties of color images are excellent and printed images of high quality are obtained because a dye is used. Further, the third reason is that the ink has excellent storage stability.
However, when using aqueous inks using aqueous dyes as coloring agents, water resistance of printed images is poor.
Further, with the improvements in document productivity in offices, and the like, increases in printing speed are required and jetting frequency response in a high frequency driving range also becomes important in ink jet recording.
Various studies and developments have been carried out to improve water resistance and jetting frequency response of such aqueous dyes.
For example, Japanese Patent Application Laid-Open (JP-A) Nos. 2-29687 and 2-255876 suggest a method for improving the water resistance of ink by adding a polyamine to it. However, in the case of such an ink, the solubility stability of a dye becomes more easily lowered due to mutual action with the polyamine, and viscosity is increased because of the reaction of the polyamine over time. Therefore, clogging can occur and ink discharge stability decreases.
Further, JP-A Nos. 3-91577, 4-226175, 4-233975, 4-270286, 4-279671, and 6-93196 present a method for improving water resistance of ink by using a dye having a carboxyl group. However, in the case of such an ink, the dissolubility of a dye is reduced due to volatilization of water and/or an ammonium ion which is a counter ion. Clogging occurs and preservability of the ink tends to be lowered. Further, in the case of thermal ink jet recording, deposition on the surface of a heater referred to as "kogation" is occurs easily and changes in the discharge ability of ink increase over time.
To reduce these problems, which occur with an increase in water resistance, in JP-A No. 4-226175, there are methods suggested in which dyes with similar structures are mixed, a method in which a pH buffering agent is added to an ink, and method in which aphosphate is added. However, in these cases, even though pH can be stably maintained, the improvement in clogging is not sufficient, and the improvement in kogation which is a problem in thermal ink jet recording is also insufficient.
Also, JP-A No. 7-26178 suggests a method in which an alkaline metal compound is added to ink as a method which copes simultaneously with problems which occur with the improvement of water resistance and with the jetting frequency response. However, even though such an ink can improve clogging if the storage period is short, when the ink is stored for a long time, the solubility of a dye is decreased, and ink storage stability deteriorates. Further, jetting frequency response when high frequency is used is not satisfactory, and voids and white streaks occur easily. Moreover, the ink cannot improve kogation which is problematical in thermal ink jet recording.
Further, JP-A No. 7-166116 suggests an ink containing a combination of an amine compound and a substituted aromatic compound, and the like. However, in this case, since the dissolved condition of the substituted aromatic compound added is unstable, clogging tends to deteriorate, and the adhesion position of droplets during printing is disturbed so that image quality deterioration and other problems arise. At the same time, since the molecular weight of amine compounds added is high, the jetting frequency response is not satisfactory, and when driven at high frequency, voids and white streaks occur. Moreover, kogation which is problematical in thermal ink jet recording is not reduced.
As described above, no ink jet recording ink has been obtained which has superior water resistance and provides the various abilities required of an ink jet recording ink.